The present invention relates to proportional solenoid valves and in particular to a vacuum regulator that is particularly adapted for use on automotive vehicles of the type having a computer-controlled exhaust gas recirculation system.
Present day emission equipment on automobiles includes an exhaust gas recirculation, or EGR, system which returns a portion of the exhaust gases to the intake system of the engine. The amount of exhaust gases introduced into the intake system is controlled by a vacuum-actuated EGR valve. The EGR valve is connected between the engine exhaust system and the intake system. The degree of opening of the EGR valve and hence the amount of exhaust gases that are introduced into the intake system is determined by the vacuum signal supplied to the EGR valve. The vacuum signal is regulated by an electrically controlled vacuum regulator valve which is in turn controlled by the engine management computer. In particular, the vacuum regulator is adapted to control the amount of vacuum provided to the EGR valve in accordance with the electrical signal supplied to the regulator by the engine control computer.
Because the vacuum regulator valve is a proportional device, it is important that the regulator be precisely calibrated so that a specified current signal from the engine control computer results in a predetermined amount of negative vacuum pressure being supplied to the EGR valve. Heretofore, vacuum regulators of this type have been calibrated after assembly by energizing the solenoid coil of the regulator with a preselected current signal and adjusting the dimension of the working or primary air gap between the pole piece and the armature until a predetermined vacuum output is achieved. Thereafter, the position of the pole piece and/or the armature is fixed to secure the calibration. A vacuum regulator of this type is disclosed in U.S. Pat. No. 4,567,910 to Slavin et al. and assigned to the assignee of the present invention.
The primary disadvantage of this approach is the highly sensitive nature of the calibration process and the resulting degree of variation in the output of the vacuum regulator to extremely small variations in the actual dimension of the working air gap. Moreover, because of the extremely sensitive nature of the known calibration techniques, it is necessary to perform the calibration adjustment very slowly to avoid overshooting the desired set point. Consequently, the required production time and hence the associate production cost of each unit produced in this manner is increased. In addition, due to such factors as component resiliency, it can be extremely difficult to precisely hold the desired set calibration point, thereby resulting in a unit that produces a different output than that observed when the unit was calibrated.
Accordingly, it is the primary object of the present invention to overcome the disadvantages of the prior art and provide an improved vacuum regulator having a less sensitive means of calibration. In particular, the vacuum regulator according to the present invention is calibrated by adjusting the dimension of a secondary air gap provided in the flux path of the solenoid. Because dimensional variations in the secondary air gap of the solenoid have a less dramatic impact on the operation of the solenoid than dimensional variations in the primary air gap between the pole piece and armature, the sensitivity of the present calibration process is substantially reduced.
In general, this is accomplished by providing a vacuum regulator with a solenoid structure having an adjustable secondary air gap in the flux path of the solenoid at the opposite end of the pole piece from the armature. This allows the primary air gap at the armature end of the pole piece to be set consistently from piece to piece thereby minimizing variations in both the magnetic forces on the armature and in the air flow path through the pole piece and across the face of the armature. Moreover, the secondary air gap provided in the preferred embodiment of the vacuum regulator according to the present invention is designed to divide the flux path of the solenoid so that a portion of the magnetic flux crosses a nonadjustable air gap and the remainder of the flux crosses the adjustable air gap. In this manner, the sensitivity of the calibration process is further reduced, thereby enabling more accurate settings with less chance of overshooting the desired set point. Consequently, the rate of production of vacuum regulators according to the present invention is improved.
Additional objects and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiment which makes reference to the accompanying drawings in which: